1. Technical Field of the Invention
This invention relates to the preparation of ketone derivatives of polyoxypropylene glycols. More particularly, this invention relates to a method wherein the terminal hydroxyl groups of a polyoxypropylene glycol are oxidized to ketone groups. Still more particularly, this invention is directed to a method wherein a polyoxypropylene glycol is brought into contact with a hypochlorite oxidant in the presence of a catalytically effective amount of a ruthenium catalyst and a halogenated alkane solvent in order to substantially selectively convert the hydroxyl groups of the polyoxypropylene glycol to terminal ketone groups. The ketone terminated derivatives of polyoxypropylene glycols are useful as intermediates for the preparation of a wide variety of products. For example, they may be reacted with amines to provide fuel additives or converted to carboxylic acids to provide surfactants.
2. Prior Art
It is known to react secondary alcohols and primary benzyl and allyl alcohols to the corresponding ketones and aldehydes in the presence of an oxidant such as Cu(NP.sub.3).sub.2 or Zn(NO.sub.3).sub.2 supported on silica gel in the presence of an aliphatic hydrocarbon solvent or a chlorinated aliphatic hydrocarbon solvent as shown, for example, by a paper by Takeshi Nishiguchi and Fumi Asano entitled "Oxidation of Alcohols by Metallic Nitrates Supported on Silica Gel" (J. Org. Chem. 1989, 54, 1531-1535).
Willis et al. U. S. Pat. No. 4,233,460 discloses a process for converting alkoxyalkanols to the corresponding acids by reacting the alcohol with an alkali metal hydroxide and a tertiary butyl hydroperoxide in the presence of a catalytic amount of palladium. The oxidation of polyethylene glycols to dicarboxylic acids is disclosed by Morris et al. in U. S. Pat. No. 4,256,916 wherein it is disclosed that polyethylene glycols can be converted to the corresponding carboxylic acids by oxidation in an aqueous solution over a fixed bed of a catalyst consisting of platinum on a granular carbon support.
Stutts et al. U. S. Pat. No. 4,488,944 discloses the preparation of dicarboxylic acids by the oxidation of polyalkylene glycols with electrochemically generated nickeloxide hydroxide.
U. S. Pat. No. 3,479,403 to MacLean discloses that ruthenium can be used as an oxidation catalyst and that activity is enhanced by maintaining the oxidation potential of the ruthenium catalyst at less than the oxidizing potential of Ru(VIII) to greater than that of Ru(IV). In Example I, the oxidation of ethanol to acetic acid by the slow addition of an aqueous solution of calcium hypochlorite to an aqueous solution of ethanol containing a ruthenium chloride catalyst is disclosed. It is also disclosed in this example that the ruthenium chloride was oxidized to ruthenium tetraoxide. The oxidation of isopropanol to acetone with sodium hypochlorite in the presence of a ruthenium trichloride catalyst is also disclosed in Table II of the patent.
Barak et al. in a paper entitled "Selective Oxidation of Alcohols by a H.sub.2 O.sub.2 -RuCl.sub.3 System under Phase-Transfer Conditions" (J. Org. Chem., 1988, Vol. 53, pp. 3553-3555) discloses in part that secondary alcohols can be oxidized to ketones with one hundred percent selectivity when using hydrogen peroxide as the oxidizing agent. Wolfe et al. disclose in an article entitled "Ruthenium Trichloride-catalysed Hypochlorite Oxidation of Organic Compounds" (Chemical Communications, 1970, pp. 1420-1421) disclose that in the catalytic hypochlorite oxidation of organic compounds with ruthenium trichloride, the ruthenium trichloride is oxidized to ruthenium tetraoxide.
A paper entitled "Fast and Selective Oxidation of Primary Alcohols to Aldehydes or to Carboxylic Acids and of Secondary Alcohols to Ketones Mediated by Oxoammonium Salts under Two-Phase Conditions" by Anelli et al. (J. Org. Chem., 1987, Vol. 52, pp. 2559-2562) discloses oxidation of a variety of alcohols in solution in methylene chloride with sodium hypochlorite.
In all of the prior art references (and in references not cited here) oxidation of polyalkylene glycols has always been on polyethylene glycols. As far as we are aware, there are no references on the oxidation of a polypropylene glycol to diketones. This is especially surprising in view of the fact that lower molecular weight secondary alcohols have been oxidized to ketones.